User Equipment or tell (UE) of Machine Type Communication (MTC), also called Machine to Machine (M2M) user communication device, is the current major application type of the Internet of Things. In the technical report TR45.820V200 of the 3rd Generation Partnership Project (3GPP), several technologies that are applicable to Cellular Internet of Things (C-IOT) are published; among them, the technology of Narrow Band Long Term Evolution (NB-LTE) attracts the most attention. The bandwidth of NB-LTE system is 200 kHz, the same as the channel bandwidth of Global System for Mobile Communication (GSM). This brings great convenience for GSM frequency spectrum being reused on NB-LTE system as well as reducing mutual interference with nearby GSM channels. Besides, the emission bandwidth of NB-LTE system and the interval of downlink subcarrier are 180 kHz and 15 kHz respectively, which are respectively the same as the bandwidth and subcarrier spacing of a Physical Resource Block (PRB) on LTE system. Therefore, it is favorable for the relevant design of reusing related LTE system on NB-LTE. It is also good for reducing the mutual interference between the two systems when the reused GSM frequency spectrum on NB-LTE is next to the frequency spectrum of LTE system.
Moreover, LTE system supports the following 6 system bandwidths: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz, and these 6 bandwidths have respectively 72, 150, 300, 600, 900, and 1200 subcarriers available. Considering that the emission bandwidth of NB-LTE system and the interval of downlink subcarrier are respectively the same as the bandwidth and subcarrier spacing of a PRB on LTE system, it is possible that NB-LTE and LTE are existed on the same portion of frequency spectrum; for example, allocating a 180 kHz bandwidth used for NB-LTE signal emission on LTE system of 20 MHz bandwidth. However, the related technologies of how to transmit critical signals of; e.g. synchronization signal, pilot signal, and etc., on NB-LTE in order to achieve signal detection and cost reduction for the terminal of NB-LTE system service as well as reduce the mutual interference between the two systems still lack of effective solutions due to the terminal differences between NB-LTE and LTE systems.